High-efficiency radio frequency (RF) systems are desired in portable battery-operated wireless communication. With modern wireless systems, modulation format has a high envelope peak-average ratio (PAR) and linear power amplifiers being implemented have low average efficiency. In the emerging millimeter wave (mmW) systems (e.g., WiGig and 5G), a power efficiency drops even more due to a higher back-off for linearity and an initial low efficiency of the power amplifier at mmW frequency bands. The spectrum between 30 GHz and 300 GHz, for example, can be referred to as the millimeter wave band because the wavelengths for these frequencies are about one to ten millimeters. Different techniques, such as with envelope tracking (ET) and polar digital transmitters to boost PA efficiency show some promise at low frequency and moderate data rates of tens of MHz, but become ineffective at mmW and with Gb/s rates.